linux-kernel - Re: [PATCH 1/1] usb: ulpi: don't register drivers if bus doesn't exist

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Date:	Sun, 24 May 2015 09:26:16 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Lu Baolu <baolu.lu@...ux.intel.com>
Cc:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	David Cohen <david.a.cohen@...ux.intel.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] usb: ulpi: don't register drivers if bus doesn't
 exist

On Thu, May 21, 2015 at 04:57:52PM +0800, Lu Baolu wrote:
> ULPI registers its bus at module_init, so if the bus fails to register, the
> module will fail to load and all will be well in the world.
> 
> However, if the ULPI code is built-in rather than a module, the bus
> initialization may fail, but we'd still try to register drivers later onto
> a non-existent bus, which will panic the kernel.
> 
> Fix that by checking that the bus was indeed initialized before trying to
> register drivers on top of it.
> 
> Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
> Signed-off-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Reported-by: Zhuo Qiuxu <qiuxu.zhuo@...el.com>
> Reviewed-by: David Cohen <david.a.cohen@...ux.intel.com>
> ---
>  drivers/usb/common/ulpi.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/common/ulpi.c b/drivers/usb/common/ulpi.c
> index 0e6f968..af52b46 100644
> --- a/drivers/usb/common/ulpi.c
> +++ b/drivers/usb/common/ulpi.c
> @@ -132,6 +132,10 @@ int ulpi_register_driver(struct ulpi_driver *drv)
>  	if (!drv->probe)
>  		return -EINVAL;
>  
> +	/* Was the bus registered successfully? */
> +	if (unlikely(WARN_ON(!ulpi_bus.p)))

never use unlikely/likely unless you can actually measure the difference
if the marking is not used.

Hint, on driver probe time, you can't.

thanks,

greg k-h
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